1. Field of the Invention
The present invention relates generally to integrated circuits and more specifically to a low resistant metallic ground grid for integrated circuits.
2. Description of the Prior Art:
The ever-increasing complexity of integrated circuits has lead to large chip sizes. One problem with these large circuit areas is the resistant drop in the ground metallization line between the ground pad and all other ground points in the circuit. Many times the ground line's resistance is significant enough to cause ground voltage drop problems in some junction isolated circuits.
In junction isolated circuits having substantial amounts of current flowing in the substrate, the ground line is only part of the consideration. The current flowing in the substrate has to also flow through a highly resistive isolation diffusion until it can get into the metallized ground line through conveniently placed ground tap, which is common to the metallized ground line and the isolated diffusion.
The prior art provides generally a ground path by diffusion into the semiconductive body of the integrated circuit or by a metal ground conductor formed on an insulating layer on the surface of the integrated circuit. In order to keep the resistance per square relatively small, the diffused ground paths are generally made wide, thus reducing the packing density of the integrated circuit. The metal ground conductors of the prior art are difficult to form on uneven surfaces of the integrated circuit without breaking or having pinholes and without shorting out other portions of the integrated circuit through imperfections in the insulating layer. Also, the metal ground conductor of the prior art requires the formation of a surface insulating layer at all points at which metal interconnects must crossover. This is not only responsible for the increase in expense of the integrated circuit, but also adds restraint to the circuit layout.